High performance semiconducting devices are continuously being redesigned in order to increase processing speed and/or power. Each increase in processing speed and power generally carries a cost of increased size such that additional innovations must be made in order to minimize the size of the semiconducting devices. Manufacturers of semiconducting devices continually try to improve product performance and reduce product size while minimizing production costs.
Several methods have been employed to minimize the size of semiconducting devices. One method includes stacking multiple dice onto a substrate that electrically connects one or more of the stacked dice to other electronic components which make up part of an electronic system.
Some of the dice within the stack may include active circuitry that is exposed on the upper surface of the die (e.g., a flash memory array). The active circuitry on the upper surface of the die is slightly larger (e.g., approximately 1 mm) than the spacer on all four sides of the spacer such that wires can be bonded to the active circuitry on all four sides of the spacer.
One drawback with such a spacer design is that the spacer places the exposed active circuitry under stress that varies relative to the position of the active circuitry on the die, especially where the active circuitry coincides with the edges of the spacer. The varying stress at different positions across the upper surface of the die causes the transconductance (gm) of the die to change at different positions on the die.
In an example semiconducting device where the active circuitry on the die includes a flash memory array, the outer blocks of the flash memory array (i.e., those blocks near the edge of the spacer) are typically at a significantly different stress than the blocks near the center of the array. This variation in the stress causes a gm degradation on the outer blocks of the array relative to the center blocks due to the location of the edge of the spacer. The gm degradation of the outer blocks relative to the center blocks causes decreased program erase (P/E) cycling performance within the flash memory array.
In another example semiconducting device where the active circuitry on the die includes logic circuitry, there is also gm degradation due to the location of the edge of the spacer. The gm degradation may result in timing failures due to transistor current changes within the logic circuitry.